TUESDAY, April 24 (HealthDay News) -- After two decades of steadily increasing rates of childhood obesity, at least one state may finally be turning things around.

The rates of obesity in children under the age of 6 in eastern Massachusetts declined during the period between 2004 and 2008, according to a new study.

The researchers also found that the rates of obesity declined more for children who were insured by non-Medicaid health plans.

"In this analysis, we found a substantial decline in obesity prevalence among young children during 2004 to 2008. However, the smaller decrease in obesity prevalence in Medicaid-insured children suggests that the coming years may see a widening of socioeconomic disparities in childhood obesity," wrote the study's authors.

Nutritionist Nancy Copperman, director of public health initiatives at the North Shore-LIJ Health System in Great Neck, N.Y., commented on the new findings.

"This study shows some promise that we might be turning the tide on childhood obesity. What isn't clear is if this decline is from the things we're doing to prevent obesity [that] are causing the change they see," Copperman said.

Results of the study are to be published in the May issue of Pediatrics, but were released online April 23.

Between 1980 and 2001, there was a rapid increase in the prevalence of childhood obesity, according to background information in the study. However, most recent national studies have shown that childhood obesity may be leveling off, or in some cases, even on the decline.

Targeting obesity prevention efforts at the youngest children -- those under 6 years old -- may be the most effective, as children at that age are still predominantly influenced by their parents and what their parents eat, and their lifestyle habits are just developing and may be easier to change, according to the study.

To see what was happening to childhood obesity rates for this youngest age group, the researchers reviewed data on more than 300,000 children who were seen for well-child visits between 1980 and 2008 at Harvard Vanguard Medical Associates, a multi-site pediatric practice in Eastern Massachusetts. The current analysis includes data on 36,827 youngsters who visited their physicians between 1999 and 2008.

Over time, the racial make-up of the study sample changed somewhat. In 1999-2000, nearly 64 percent of the group was non-Hispanic white. By 2007-2008, that number was about 58 percent. The number of black children at the start of the study was roughly 18 percent compared with 13.5 percent at the end of the study. The number of Asian- American children increased during the study from nearly 6 percent to nearly 13 percent.

During the period between 1999 and 2003, the researchers found that the rates of obesity remained relatively stable among the children. However, between 2004 and 2008, the rate of obesity in boys went from 10.5 percent to about 9 percent. In girls, it went from 9 percent to about 6 percent, according to the study.

In both boys and girls, the decline in obesity was more significant for children who were insured by health plans other than Medicaid, the study reported.

The researchers said they don't know exactly what caused this drop, but suspect that reduced maternal smoking during pregnancy, increased rates of breast-feeding, more limited television advertising of sweet foods to young children, and increased screening and counseling for childhood obesity may have all played a role.

"I think this study is great news. It's great that the rate is going down overall, but I haven't noticed a decrease in younger children here, where most of the children are on Medicaid," said pediatric nutritionist Lauren Graf at Montefiore Medical Center in New York City.

"When families are struggling financially, it's hard to focus on healthy foods. Many families don't have a lot of money to buy or cook food, and families don't always get the right messages from the things that are subsidized," Graf said. For example, she said, the Women, Infants and Children (WIC) food program provides vouchers for free juice, but drinking sweetened beverages such as juice is a major source of excess calories. She said many families don't realize that too much juice can be bad.

Both Copperman and Graf said the age group studied here is critical, because this is when taste preferences are developing. "Someone who's never had vegetables probably won't like broccoli if they try it for the first time at 7 or 8. When we're young is when taste preferences form, and it's also a time when families have more control. It's the time to establish good dietary habits, and to turn the TV off," Copperman said.

Both experts also said that parents need to be an example of healthy eating behavior for their children.